I. Field
This disclosure relates to the field of microelectronics. More particularly, this disclosure relates to contacting structures for semiconductor materials and methods for fabrication of such structures.
II. Description of Related Art
Efficient and balanced injection of both electrons and holes is desirable in the operation of bipolar devices and/or electronic devices where complementary charge carriers are required, such as light-emitting diodes and complementary (e.g., n-type and p-type) transistors. In certain organic devices (e.g., organic light-emitting diodes (OLEDs)) this objective is achieved through the use of different materials for forming electrical contacts. In such approaches, a first material may be used to form an anode of the organic device while a second material may be used to form a cathode of the organic device.
However, the use of different contact metals in OLEDs does not consistently provide for efficient charge injection into wide bandgap organic materials (e.g., materials with a bandgap>3 eV). Such materials may be used, for instance, in blue light emitters. In order to achieve efficient electron injection with such wide bandgap materials, low work-function metals are used to promote efficient electron injection. Such approaches have certain drawbacks, however. For instance, such low work-function materials are highly reactive, which makes them difficult to process. Typically, such materials are processed in a vacuum. A further drawback is that such low work-function materials must be encapsulated in order to prevent degradation after removal from a vacuum environment in which they are processed (e.g., deposited, patterned, etc.).
In other devices, such as organic light-emitting thin-film transistors (OLETFTs), electrons and holes are injected into the transistor channels simultaneously during operation. The ohmic contacts for such OLETFTs are usually deposited using a shadow mask. Deposition of two different contact materials (e.g., different metals) requires, for the deposition of the second material, positioning the corresponding shadow mask, which may be the same mask used for the first material or a second mask, with greater precision than the channel length of the OLETFTs. Such precise positioning is an extremely difficult task for devices with channel lengths of a few micrometers or smaller. Thus, such processes may experience significant yield loss due to alignment issues associated with such an approach. Such yield loss would result in a corresponding increase in the cost of producing such devices.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.